|Biocrude from Nannochloropsis. Credit: Savage Lab. Click to enlarge.|
A team led by Prof. Phillip Savage at the University of Michigan has found that with appropriate parameters, hydrothermal liquefaction (HTL) can convert 65% of wet algae (a Nannochloropsis species) into biocrude in one minute. The team, which has been investigating HTL processing of algae to biocrude—along with techniques for dexoygenating the product for subsequent refining—for several years, presented its latest results at the 2012 American Institute of Chemical Engineers (AIChE) Annual Meeting in Pittsburgh.
An hydrothermal process is one that involves water at elevated temperatures and pressures; hydrothermal liquefaction (HTL) is one of a number of methods for converting biomass conversion to biofuels or biofuel precursors. HTL avoids energy-intensive drying steps, and is thus more energy efficient for biomass with very high moisture content—such as microalgae—the researchers note.
To make their one-minute biocrude, Savage and Julia Faeth, a doctoral student in Savage’s lab, filled a steel pipe connector with 1.5 milliliters of wet algae, capped it and plunged it into 1,100-degree Fahrenheit sand. Previously, Savage and his team heated the algae for times ranging from 10 to 90 minutes. They saw their best results, with about half of the algae converted to biocrude, after treating it for 10 to 40 minutes at 570 degrees.
Savage suggests that the one-minute results are so much better perhaps because the reactions that produce biocrude are actually must faster than previously thought. Faeth suggests that the fast heating might boost the biocrude by keeping unwanted reactions at bay.
The team points out that shorter reaction times mean that the reactors don’t have to be as large, and costs could potentially be lower.
Most current commercial makers of algae-based fuel first dry the algae and then extract the natural oil, but the cost is high--more than $20 per gallon.
Companies know that that approach is not economical, so they are looking at approaches for using wet algae, as are we.Phillip Savage
One of the advantages of the wet method is that it also breaks down proteins and carbohydrates. The “minute method” did this so successfully that the oil contained about 90% of the energy in the original algae—near the upper bound of what is possible, according to Savage.
On the upgrading side, the Savage lab earlier this year produced a biocrude that was 97% carbon and hydrogen; a paper on this work is currently under review.
The research was funded by the Emerging Frontiers in Research and Innovation program of the National Science Foundation. The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.
Julia L. Faeth and Phillip E. Savage (2012) The Effects of Heating Rate and Reaction Time On Hydrothermal Liquefaction of Microalgae. AIChE 2012
Valdez, P.J., Dickinson, J.G., Savage, P.E. (2011) Characterization of product fractions from hydrothermal liquefaction of Nannochloropsis sp. and the influence of solvents, Energy & Fuels 25 3235-3243 doi: 10.1021/ef2004046
Peigao Duan and Phillip E. Savage (2011) Hydrothermal Liquefaction of a Microalga with Heterogeneous Catalysts. Ind. Eng. Chem. Res. 50 (1), pp 52–61 doi: 10.1021/ie100758s